Enhanced underwater wireless optical communication system energy harvesting method based on time switching mode

Abstract

The invention discloses an enhanced underwater wireless optical communication system energy harvesting method based on a time switching mode, and belongs to the technical field of underwater wireless optical communication. A current signal received by a solar cell panel serving as an underwater photoelectric receiver is divided into two sections according to a total working time period Ttot, one section tau Ttot is used for information decoding, the other section (1-tau) Ttot is used for special energy collection, and tau is a time division factor. In an information decoding time period tau Ttot, the AC / DC separation device recovers a DC bias component item which is originally discarded in the received current signal, and the remaining AC signal item is used for information decoding; and the direct-current component recovered at the time period and the special energy harvesting item in the special energy harvesting time period (1-tau) Ttot are sent to an energy harvester together for total energy collection, so that energy harvesting efficiency which is more efficient than that of a traditional time switching (TS) mode is obtained. According to the enhanced underwater wireless optical communication system energy harvesting method based on the time switching mode provided by the invention, the energy of the discarded direct current component in the information decoding module in the decoding time period can be recycled and reused, so that more energy can be harvested under different threshold spectrum efficiencies compared with a traditional TS (Transport Stream) method.

Description

Technical Field

[0001] The present invention belongs to the technical field of wireless optical communication and relates to an enhanced energy harvesting scheme suitable for an underwater wireless optical communication (UWOC) system in a "information-power" joint transmission process. Background Art

[0002] Underwater wireless optical communication based on the "blue-green" visible light band has many technical advantages in high data transmission rate and low latency, and has shown great application potential in underwater wireless communication. Different from the traditional working mode of terrestrial wireless cellular networks that rely on power lines for power supply, in the process of underwater wireless optical communication (UWOC), batteries are generally used to provide power for communication nodes and other devices. However, traditional charging or replacement of batteries in complex underwater environments often consumes a lot of manpower and material resources, so it is necessary to directly obtain energy from the external or natural environment to meet the energy requirements for the normal operation of underwater equipment.

[0003] In 2021, Murat Uysal et al. proposed a joint transmission scheme for synchronous transmission of optical information and power for underwater wireless optical communication systems (see their paper "SLIPT for underwater visible lightcommunications: performance analysis and optimization", IEEE Trans. on Wireless Communications, Vol. 20, No. 10, 2021). Among them, in the time switching (TS) mode of this scheme, the receiving end switches the working time between energy collection and information decoding to maximize the system energy harvesting under the constraints of ensuring certain bit error rate and spectrum efficiency. Its specific working principle is: when the receiver is in the energy collection period, the DC bias of the signal is set to the maximum value, and the transmission signal is suppressed, that is, it does not carry any information, thereby maximizing the energy collection efficiency; when the receiver is in the information decoding period, the DC component of the signal is filtered, and the AC part containing the signal term is used for information decoding. This repeated time alternation can realize the joint transmission of underwater optical information and power.

[0004] In the time-switching (TS)-based "information-power" joint transmission method proposed by Uysal (which we call the "traditional TS method"), the DC bias exists not only in the energy collection module, but also in the information decoding module. However, in his scheme, usually only the DC bias in the energy collection module is used for energy collection, while the DC bias in the information decoding module is discarded, which obviously leads to a loss in energy collection efficiency. Therefore, it is necessary to recycle and reuse the discarded DC bias in the information decoding module period in the traditional TS scheme to further improve the energy collection efficiency of the entire system. Summary of the invention

[0005] Purpose of the invention: In order to solve the problem of how to obtain effective energy replenishment when the UWOC system works underwater, the present invention proposes an enhanced energy harvesting method for the UWOC system based on the time switching (TS) mode. This scheme collects energy from the DC biased optical signal. Compared with the traditional time switching method, it can recycle and reuse the energy of the DC component discarded in the information decoding module during the decoding time period, thereby obtaining a higher energy harvesting efficiency.

[0006] Technical solution: An enhanced energy harvesting method for an underwater wireless optical communication (UWOC) system, comprising the following steps:

[0007] Step 1: The current signal i received by the solar panel as an underwater photoelectric receiver r According to the total working time T tot Divided into two segments, one of which is τT tot For information decoding, another segment (1-τ)T tot It is used for dedicated energy harvesting, and τ is the time division factor.

[0008] Step 2: During the information decoding period τT tot , the AC / DC separation device will receive the current signal i r The DC bias component originally discarded in the process is recovered, and the remaining AC signal term is used for information decoding; the DC component recovered during this period is the same as the dedicated energy collection period (1-τ)T tot The dedicated energy harvesting items are sent to the energy harvester for total energy collection, thereby achieving more efficient energy harvesting efficiency than the traditional time switching (TS) mode.

[0009] As a preferred solution, the mathematical expression of the current signal received by the UWOC system is:

[0010] i r =rIhSB+rIhSx+n=rIhS(B+x)+n

[0011] In the above formula, r is the responsivity of the solar panel, that is, the light-to-electricity conversion efficiency; I is the turbulence attenuation coefficient, and its statistical characteristic probability density function (PDF) is f I (I); h is the underwater channel path loss coefficient; S is the slope of the laser diode, that is, the current-to-power conversion coefficient; B is the signal DC bias; x is the M-ary pulse amplitude modulation (M-PAM) signal sent by the transmitter, and x = (m-1)A / (M-1), m = 1, 2, ..., M, where A∈[0, (I H -I L ) / 2] is the maximum amplitude of the modulation symbol, I H and I L They represent the maximum and minimum values ​​of the input DC bias respectively; n is additive white Gaussian noise.

[0012] As a preferred solution, the information decoding period τT tot In the above example, the DC component that is originally discarded and recovered by the AC / DC separator is rIhSB2, where B2 = (I H +I L ) / 2.

[0013] As a preferred solution, the information decoding period τT tot In the figure, the AC signal separated by the AC / DC separator is rIhSx+n, which is used for subsequent information decoding.

[0014] As a preferred solution, the dedicated energy collection period (1-τ)T tot In the above example, the dedicated energy harvesting term is rIhSB1, where B1 = I H .

[0015] As a preferred solution, the total energy harvested by the energy harvester is

[0016]

[0017] In the above formula is the information decoding period τT tot The average energy term collected; is the dedicated energy collection period (1-τ)T tot The average energy term collected. Where F represents the fill factor, V t represents the thermal voltage, and I0 represents the dark saturation current.

[0018] As a preferred solution, the time division factor Among them, γ represents the system receiving signal-to-noise ratio, η th is the minimum spectral efficiency threshold, f I (I) is the PDF expression of the turbulence attenuation coefficient I.

[0019] As a preferred solution, the information decoding period τT tot The average energy item collected and dedicated energy harvesting period (1-τ)T tot The average energy item collected The PDF function f used to define the turbulence attenuation coefficient I in these two integral expressions is I (I) Determined by the specific ocean turbulence fading environment.

[0020] As a preferred solution, the time division factor The PDF function f used to define the turbulence attenuation coefficient I in I (I) is also determined by the specific ocean turbulence fading environment, and its expression is similar to and f I (I) Exactly the same.

[0021] Beneficial effects:

[0022] Compared with the technology adopted by the existing traditional TS method, the technical solution of the present invention has the following beneficial technical effects: the present invention provides an enhanced energy harvesting method for UWOC system based on time switching mode, which can recycle and reuse the energy of the DC component originally discarded in the information decoding module in the decoding time period, thereby harvesting more energy than the traditional TS method under different threshold spectrum efficiencies. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a block diagram of the principle implementation of an enhanced energy harvesting solution for an underwater wireless optical communication (UWOC) system based on a time switching mode proposed in the present invention.

[0024] Figure 2 It is a comparison curve of the energy harvested by the system and the spectrum efficiency of different thresholds under the optimal time division factor of the enhanced energy harvesting method based on the time switching mode proposed in the present invention and the traditional TS method. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0026] The present invention is an enhanced energy harvesting scheme suitable for the "information-power" joint transmission UWOC system. This method can be used to obtain higher energy harvesting efficiency in the underwater wireless optical communication (UWOC) system based on the time switching mode. The specific implementation method and application examples are described as follows:

[0027] Assume that the mathematical expression of the underwater received current signal is:

[0028] i r =rIhSB+rIhSx+n=nIhS(B+x)+n

[0029] In the above formula, r is the responsivity of the solar panel, that is, the light-to-electricity conversion efficiency; I is the turbulence attenuation coefficient, and its statistical characteristic probability density function (PDF) is f I (I); h is the underwater channel path loss coefficient; S is the slope of the laser diode, that is, the current-power conversion coefficient; B is the signal DC bias; x is the M-ary pulse amplitude modulation (M-PAM) signal sent by the transmitter, x = (m-1)A / (M-1), m = 1, 2, ..., M, where A∈[0, (I H -I L ) / 2] is the maximum amplitude of the modulation symbol, I H and I L They represent the maximum and minimum values ​​of the input DC bias respectively; n is additive white Gaussian noise.

[0030] Step 1: If Figure 1 As shown, the current signal i received by the underwater solar panel r Divided into τT according to working time tot and (1-τ)T tot Two time periods, where τT tot The time period is used for information decoding, and (1-τ)T tot The time period is used for special energy harvesting, where T tot Represents a total working time, and τ is the time division factor.

[0031] Step 2: During the dedicated energy harvesting period (1-τ)T tot Since there is no need for information decoding, the transmitter signal x can be completely suppressed, that is, A = 0 at this time, and the DC bias takes the maximum value B = B1 = I H , ignoring the influence of noise, the receiving end adds the DC component rIhSB1 to the energy harvester to obtain the average harvested energy Where, represents the fill factor, V t represents the thermal voltage, and I0 represents the dark saturation current.

[0032] Step 3: In the information decoding time period τT tot , because there is an optical information signal that needs to be decoded, the DC bias is B=B2=(I H +I L ) / 2, the modulation amplitude is A=(I H -I L) / 2. In the traditional TS solution, the current signal i r The DC bias term rIhSB2 in the energy harvester is directly discarded after being filtered out by the capacitor, and only the remaining AC term rIhSx+n is used for information decoding. Obviously, the discarded DC bias term rIhSB2 can be fully reused to improve the efficiency of energy harvesting. Therefore, we add an AC / DC separation module to send the DC bias term rIhSB2 to the energy harvester for recycling to obtain additional harvested average energy. The AC signal rIhSx+n continues to be used for information decoding.

[0033] Step 4: Sum the average energy harvested during the above two periods to obtain the average total energy harvested:

[0034] Step 5: Based on the average spectrum efficiency The optimal time division factor can be obtained by applying the constraints Where γ represents the system receiving signal-to-noise ratio, η th is the minimum spectral efficiency threshold. According to the optimal solution τ of the time division factor τ opt , the system can obtain the maximum value of harvested energy.

[0035] Application example of enhanced energy harvesting method for UWOC system based on time switching mode

[0036] Below, we take the final energy harvesting effect comparison simulation of the UWOC system adopting the enhanced energy harvesting scheme based on the time switching mode proposed in the present invention and the UWOC system adopting the traditional TS method energy harvesting scheme as an example to illustrate the advantages of adopting the scheme proposed in the present invention.

[0037] Figure 2 For clear ocean water, the receiver diameter D R =20cm, initial divergence angle of laser source θ F =6°, ocean turbulence attenuation PDFf I (I) obeys the log-normal distribution (turbulent scintillation index ), the UWOC system using the enhanced energy harvesting scheme proposed in the present invention and the traditional TS method energy harvesting scheme has the optimal time division factor τ corresponding to each spectrum efficiency inspection point opt Under the premise of th To gain a more intuitive understanding, we selected several representative spectrum efficiency thresholds in the figure to obtain the harvested energy values ​​and compiled them into the following Table 1.

[0038] Table 1 Energy harvested by the UWOC system

[0039]

[0040] From the results in the table, it can be found that under different threshold spectrum efficiencies, the energy harvested by the UWOC system using the proposed enhanced energy harvesting scheme is indeed significantly improved compared to the energy harvested by the UWOC system using the traditional TS energy harvesting scheme. This shows that the energy harvesting scheme proposed in the present invention has a better energy collection effect.

[0041] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An enhanced energy harvesting method for an underwater wireless optical communication (UWOC) system, characterized in that: The steps include: Step 1: The current signal i received by the solar panel as an underwater photoelectric receiver r According to the total working time T tot Divided into two segments, one of which is τT tot For information decoding, another segment (1-τ)T tot It is used for dedicated energy harvesting, and τ is the time division factor; Step 2: During the information decoding period τT tot , the AC / DC separation device will receive the current signal i r The DC bias component originally discarded in the process is recovered, and the remaining AC signal term is used for information decoding; the DC component recovered during this period is the same as the dedicated energy collection period (1-τ)T tot The dedicated energy harvesting items are sent to the energy harvester for total energy collection, thereby achieving more efficient energy harvesting efficiency than the traditional time switching (TS) mode.

2. The UWOC system enhanced energy harvesting method according to claim 1, characterized in that: The mathematical expression of the current signal received by the UWOC system is: i r =rIhSB+rIhSx+n=rIhS(B+x)+n In the above formula, r is the responsivity of the solar panel, that is, the light-to-electricity conversion efficiency; I is the turbulence attenuation coefficient, and its statistical characteristic probability density function (PDF) is f I (I); h is the underwater channel path loss coefficient; S is the slope of the laser diode, that is, the current-to-power conversion coefficient; B is the signal DC bias; x is the M-ary pulse amplitude modulation (M-PAM) signal sent by the transmitter, and x = (m-1)A / (M-1), m = 1, 2, ..., M, where A∈[0, (I H -I L ) / 2] is the maximum amplitude of the modulation symbol, I H and I L They represent the maximum and minimum values ​​of the input DC bias respectively; n is additive white Gaussian noise.

3. The UWOC system enhanced energy harvesting method according to claim 1, characterized in that: The information decoding period τT tot In the above example, the DC component that is originally discarded and recovered by the AC / DC separator is rIhSB2, where B2 = (I H +I L ) / 2.

4. The UWOC system enhanced energy harvesting method according to claim 1, characterized in that: The information decoding period τT tot In the figure, the AC signal item separated by the AC / DC separator is rIhSx+n, which is used for subsequent information decoding.

5. The UWOC system enhanced energy harvesting method according to claim 1, characterized in that: The dedicated energy collection period (1-τ)T tot In the above example, the dedicated energy harvesting term is rIhSB1, where B1 = I H .

6. The UWOC system enhanced energy harvesting method according to claim 1, characterized in that: The total energy harvested by the energy harvester is In the above formula is the information decoding period τT tot The average energy term collected; is the dedicated energy collection period (1-τ)T tot The average energy term collected. Where F represents the fill factor, V t represents the thermal voltage, and L0 represents the dark saturation current.

7. The UWOC system enhanced energy harvesting method according to claim 1, characterized in that: The time division factor Among them, γ represents the system receiving signal-to-noise ratio, η th is the minimum spectral efficiency threshold, f I (I) is the PDF expression of the turbulence attenuation coefficient I.

8. The UWOC system enhanced energy harvesting method according to claim 6, characterized in that: The information decoding period τT tot The average energy item collected and dedicated energy harvesting period (1-τ)T tot The average energy item collected The PDF function f used to define the turbulence attenuation coefficient I in these two integral expressions is I (I) Determined by the specific ocean turbulence fading environment.

9. The UWOC system enhanced energy harvesting method according to claim 7, characterized in that: The time division factor The PDF function f used to define the turbulence attenuation coefficient I in I (I) is also determined by the specific ocean turbulence fading environment, and its expression is the same as f in claim 8. I (I) The same.

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